1. Field of the Invention
The invention relates to a curable composition for optical imprinting, a pattern forming method, a fine pattern, and a method for manufacturing a semiconductor device. Specifically, the invention relates to a curable composition for optical imprinting for forming a fine pattern using photoirradiation used for manufacturing a semiconductor integrated circuit, a flat screen, a micro-electromechanical systems (MEMS), a sensor element, an optical disk, a magnetic recording medium such as a high density memory disk, an optical component such as a diffraction grating or a relief hologram, a nano device, an optical device, an optical film or a polarizing element for manufacturing a flat panel display, a thin film transistor of a liquid crystal display, an organic transistor, a color filter, an overcoat layer, a column member, a rib material for liquid crystal orientation, a microlens array, an immunological analyzing chip, a DNA separation chip, a microreactor, a nano-bio device, an optical waveguide, an optical filter, and a photonic liquid crystal.
2. Description of the Related Art
The imprinting method is a technique of precisely transferring a fine pattern by pressing a mold standard (generally referred to as a mold, a stamper, or a template), which is obtained by forming an uneven pattern by developing an embossing technology well-known in an optical disc production, to a resist and dynamically deforming the mold standard. If the mold is once manufactured, a fine structure such as a nanostructure can be repeatedly molded in a simple way. Therefore, the mold is economical and, recently, an application thereof in various fields is expected.
As an imprinting method, a heat imprinting method (for example, see S. Chou et al., Appl. Phys. Lett. 67, 3114 (1995)) using a thermoplastic resin as a workpiece and an optical imprinting method (for example, see M. Colbun et al., Proc. SPIE 3676, 379 (1999)) using a curable composition are suggested. The heat imprinting method is a method of pressing a mold to a polymer resin heated to the glass transition temperature or higher, cooling the mold to a glass transition temperature or less, and releasing the mold, such that a fine structure is transferred to the resin on the substrate. This method is extremely simple and can be applied to various resin materials or various glass materials.
Meanwhile, the optical imprinting method is a method of performing photoirradiation through a light transmitting mold or a light transmitting substrate, photocuring a curable composition, and separating the mold such that a fine pattern is transferred to a photocured product. This method makes imprinting possible in room temperature, and thus this method can be applied to a precision processing field of an ultrafine pattern for manufacturing a semiconductor integrated circuit or the like. Recently, new developments such as a nano-scanning method in which advantages of the both are combined or a reversal imprinting method for manufacturing a three-dimensional laminate structure are reported.
In this imprinting method, applications as below are suggested.
A first application is that a molded shape (pattern) itself has a function, and is used as an element component or a structural member of nanotechnologies. Examples thereof include structural members of various types of a micro- or nano-optical element, a high-density recording medium, an optical film, or a flat panel display.
A second application is to construct a laminate structure by integral molding of a micro structure and a nano structure or by simple interlayer position alignment and use this laminate structure for manufacturing a micro-total analysis system (μ-TAS) or a biochip.
A third application is to cause a formed pattern to be a mask and use the pattern for processing a substrate in a method such as etching. In this technique, owing to high precision position alignment and high integration, the formed pattern can be used for manufacturing high precision semiconductor integrated circuit, manufacturing a transistor of a liquid crystal display, and processing a magnetic body of a next generation hard disk called a patterned medium, instead of the lithography technique in the related art. Approaches to a practical use of the imprinting method relating to these applications are recently active.
The imprinting method has a step of separating a mold and thus releasability thereof becomes a problem in the related art. As a method of improving releasability, a method of performing a releasing treatment on a mold surface with a releasing agent such as a silane coupling agent having a perfluoro group is well-known in the art. This method decreases a surface energy on the mold surface, and thus an effect in improving releasability is excellent. However, as the imprinting is repeated, the releasing agent is deteriorated, and thus there is a problem in durability.
As an attempt for improving durability of a releasing treatment, a method of causing a silane coupling agent having a perfluoro group to be contained in the curable composition is well-known (M. Bender et al., Microelectronic Engineering 61-62, 407 (2002)). This method has a problem in that preservation stability of the curable composition is bad and defects of the imprinting pattern increase, since the silane coupling agent has reactivity in this method.
In addition, as an attempt for improving releasability, a method of causing a surfactant having a perfluoro group to be contained in a curable composition (WO2005/000552A), a method of causing a polymerizable compound having an alkyl group including two or more fluorine atoms to be contained in a curable composition (JP2010-239121A), and a method of causing a non-polymerizable compound having a polyalkylene glycol structure to be contained in the curable composition (JP2013-036027A) are well-known. In this method, the preservation stability of the curable composition which becomes a problem as the silane coupling agent can be secured.
Meanwhile, in the use of causing the ultrafine pattern to be formed with high precision in the imprinting method (for example, a use as an etching resist for processing a semiconductor substrate), an ink jet method attracts attention (JP2008-502157A). In the ink jet method, an amount of the curable composition is adjusted in response to the density of the pattern, and thus thickness unevenness of the residual film can be reduced. In addition, there is an advantage in that utilization efficiency of a material is higher than that in a spin coating method. However, if ink jet ejection is not precisely and efficiently performed, a problem of filling failure of the curable composition or film unevenness of the residual film is generated.